The present invention relates to cast concrete articles for making, for example, catch basins and manholes, and more particularly, to a novel form and method for producing cast concrete articles.
Steel forms have been used for many years to cast concrete articles for making catch basins and manholes. Manholes are typically created from multiple cast concrete sections which are configured to be stacked on top of each other. Such cast concrete articles are generally required to meet certain minimum government standards relating to the strength and permeability of the concrete. Conventionally, the cast concrete articles are produced by filling a steel form, which is similar to a mold, with a wetted mixture of, for example, cement, sand, gravel and water, which is then allowed to dry and harden. The exact mixture may vary, as is well-known in the art, and may include other components such as chemical hardening agents. These steel forms typically are used to produce cast concrete articles which weigh thousands of pounds. The steel form typically has an expandable outer jacket which surrounds an inner core. The shape of the jacket generally defines the shape of the article to be cast, which typically is hollow. The space between the core and the jacket defines the cavity of the form into which the wetted concrete mixture is disposed and cured. The cavity is filled with the wet concrete through the open top of the steel form. Additionally, a top piece, called a xe2x80x9cheader,xe2x80x9d is normally employed, after the cavity is filled, to create a xe2x80x9ctonguexe2x80x9d on the top of the cast article which can mate with a groove in the bottom of an adjoining concrete article so that such articles may be stacked on top of each other to provide for the desired depth at which the catch basin or manhole will be installed. The groove in the bottom of the article is formed by a raised wall portion on a bottom ring member over which the steel form is positioned when it is being filled with concrete. This ring member actually forms the bottom surface of the cavity which defines the shape of the concrete article.
The conventional manner of filling the steel forms with concrete is typically both labor intensive and time consuming. In general, the mixed, still wet, concrete is transported from a mixing bin to the location of the steel form. The concrete is then typically shoveled by hand from the container in which it is transported into the steel form. Because the cavity into which the wet concrete is placed may typically be only several inches wide, the filling of the mold, in customary practice, is normally done by hand since the wet concrete must be carefully filled into the relatively narrow opening at the top of the form.
Additionally, care must be taken when filling the form to ensure that air pockets do not form in the concrete. While the form is being filled with the wet concrete, steps must be taken to ensure that the concrete settles properly and any air pockets are eliminated. The conventional manner of eliminating the air pockets is to use a vibrating device, for example a xe2x80x9cstick vibrator.xe2x80x9d This device is inserted into the still wet concrete at various points around the cavity to vibrate the concrete to enhance settling and remove air pockets. Once this procedure has been performed, however, the cast concrete article is still not completed. Because the cast articles are typically stacked one on top of another to form the manhole, the top of the article is provided with a tongue portion which fits into a groove that is cast into the bottom of an adjoining article. The tongue is created using a header which is placed on top of the filled form. A header is an annular member, in the case of round forms, which has a smaller diameter wall portion offset from the outer edge of the header. The outside of the header is generally aligned with and rests on the top of the steel form. The wall portion creates a small, upstanding annular cavity around the inner core, which may only be a few inches wide, and which now must be filled with more wetted concrete to create the tongue. Once both the larger, main cavity and the smaller cavity are filled and vibrated, the surface of the concrete article must be finished by hand. Finally, the article is cured. Typically, the steel form containing the wetted concrete remains in place on the shop floor for sufficient time to cure, usually overnight. Once the concrete is cured, the outer portion of the steel form, which is typically an expandable outer jacket, is loosened from around the concrete article, by expanding the jacket, and then lifted off of the cast concrete article. Next, the concrete article is lifted off of the core and transported elsewhere for storage or shipping. The process described above is then repeated to produce additional cast concrete articles. However, due to the time needed to hand fill and then cure the articles, the process is typically performed during only one shift each work day.
As can be understood, the procedure just described, which is still the standard procedure carried out in the cast concrete manufacturing industry today, can be both time consuming and labor intensive. Most present day manufacturers of such cast concrete articles typically can have a number of steel forms which are simply set up in rows on the shop floor. To create the concrete articles, wetted concrete is delivered to each individual steel form which is then filled in the manner described above. Because of the procedure of bringing the wet concrete to the steel form, other disadvantages are encountered in the workplace. For example, the wet concrete is typically transported overhead by hydraulic devices mounted to the ceiling of the shop. The weight of the concrete and the overhead transport systems can therefore pose safety hazards to workers on the shop floor below. Additionally, spilled concrete both from the overhead transport system and from hand filling the steel forms creates tripping hazards and also requires time and effort to clean up the spilled concrete.
Accordingly, there is a need for an improved form and method for producing cast concrete articles which is faster, less labor intensive and also results in a safer and cleaner work environment.
A steel form according to the invention is provided which is generally completely sealed except for air vents and a fill port for pumping liquefied concrete into the form, thereby filling the form to produce cast concrete articles. The form can include a conventional, removable inner core surrounded by a modified jacket, which can also be expandable, and a bottom member, which can be attached to a pallet on which the steel form can be transported, for example, from the liquefied concrete pump to the kiln for drying. The fill port is preferably provided through the outer jacket. The normally open top of the steel form is sealed with a modified header, which can be internally configured to create a tongue for mating with a grooved adjoining cast concrete article. The bottom member can have a raised wall portion for forming the groove in the bottom of the concrete article which can mate with the tongue portion of an adjoining concrete article. The modified header can also include the aforementioned air vents for evacuating air as the liquefied concrete is pumped into the form. The air vents can also provide visual confirmation of the form being completely filled with concrete. Braces can be provided to support the top of the modified header against pressure as the concrete is pumped into the form. Additionally, locator bolts can be provided through the modified header, to which can be attached inserts which become embedded in the cast concrete article and can be used to facilitate the securement of manhole top sections to the cast concrete article. Furthermore, the fill port can be connected to a sliding gate arrangement wherein the fill port is movable between an open position, where the fill port aligns with an opening in the outer jacket for pumping concrete thereinto, and a closed position wherein the slide gate covers the opening in the outer jacket. After the form has been filled with liquefied concrete, the slide gate can be moved to close off the opening.
Other details, objects, and advantages of the invention will become apparent from the following detailed description and the accompanying drawing figures of certain embodiments thereof.